It is known in the art that various mercapto compounds can stabilize polyolefins and halogen-containing resins. See U.S. Pat. No. 3,144,422. It is also known from U.S. Pat. Nos. 3,364,182 and 3,801,541 that methyl methacrylate monomer can be polymerized in the presence of small amounts of a mercapto compound. It is also generally known in the art that mercapto compounds retard radical chain degradation in many types of polymers. However, even with this knowledge, there still remains a problem in finding among the many thousands of sulfur compounds the ones that most efficiently reduce the degradation of methyl methacrylate polymers. The generation of small amounts of residual monomer caused by polymer degradation during molding and extrusion results in fabricated articles that are defective and unusable. The reduced yield of acceptable articles naturally results in higher costs. In order to reduce costs, it is important to reduce as much as possible the thermal degradation of these methyl methacrylate-containing polymers.
To find a suitable stabilizer for methyl methacrylate polymers, a combination of efficiency and lack of odor and color imparted to the polymer is required. Many previously suggested thermal stabilizers are deficient in one or more of these regards, and none are as effective as those of the present invention.